1. Technical Field
The present invention relates to a method and apparatus for transmitting and receiving an image event in a video telephone.
2. Related Art
Voice over Internet Protocol (VoIP) refers to a technique of transmitting circuit-switched voice data over a packet-switched, Internet protocol (IP)-based data network, such as a local area network (LAN), a wide area network (WAN), a virtual private network (VPN), or public Internet. The VoIP provides PC-to-PC, PC-to-phone or phone-to-phone services.
VoIP began with the introduction of the Internet phone by Vocaltec Company in 1995. Software from Vocaltec Company compresses a voice signal, converts the signal into an IP packet, and transmits the packet over Internet, which can be called a PC-to-PC scheme. This scheme has a limitation in that a receiver and a sender have to access at the same time and use the same software. Since 1995, the Internet phone has been growing rapidly. Recently, a VoIP gateway, which is an interface between the Internet and public switched telephone network (PSTN), enables VoIP in a PC-to-phone or phone-to-phone scheme.
VoIP is 50% to 80% cheaper than conventional international calling, due to use of the Internet instead of the PSTN. Thus, many domestic and foreign companies are fiercely competing for the market. However, because of the nature of a packet-switching network, voice quality has still not reached a satisfactory level. Nevertheless, the Internet phone has rapidly developed with the proliferation of the Internet and technology development, and while the Internet phone is still less widely used than conventional telephone service such as a PSTN, it is likely destined to replace conventional telephone service in the future.
A video telephone data channel is composed of two real-time transport protocol (RTP) channels, which are a voice data channel and a video data channel. The voice data channel includes out-band signaling for a separate phone event process (RFC 2833) in order to receive a dual-tone multi-frequency (DTMF) signal.
In this case, if a transmitter changes state information in response to a user's state information, image data on the changed state information is transmitted to a receiver. This is because there is no definition for a video event.
There may be a case where the user changes the state information into a screen blank, standby, etc., or real-time screen data such as a camera failure or a transmission/reception error of an application program is not necessary. According to the typical VoIP video communication method, even in such a case, the image data on the state information has to be transmitted and received, and thus bandwidth is wasted. Moreover, image data occupies a tenfold wider bandwidth than general voice data, so that the waste of bandwidth is quite severe.